Wear-pattern analysis in retrieved tibial inserts of mobile-bearing and fixed-bearing total knee prostheses

Background Mobile-bearing TKAs reportedly have no clinical superiority over fixed-bearing TKAs, but a potential benefit is improved polyethylene wear behavior. Questions/purposes We asked whether extent of damage and wear patterns would be less severe on retrieved mobile-bearing TKAs than on fixed-bearing TKAs and if correlations with patient demographics could explain differences in extent or locations of damage. Methods We performed damage grading and mapping of 48 mobile-bearing TKAs retrieved due to osteolysis/loosening, infection, stiffness, instability or malpositioning. Visual grading used stereomicroscopy to identify damage, and a grade was assigned based on extent and severity. Each damage mode was then mapped onto a photograph of the implant surface, and the area affected was calculated. Results Marked wear damage occurred on both surfaces, with burnishing, scratching, and pitting the dominant modes. Damage occurred over a large portion of both surfaces, exceeding the available articular borders in nearly 30% of implants. Wear of mobile-bearing surfaces included marked third-body debris. Damage on tibiofemoral and mobile-bearing surfaces was not correlated with patient BMI or component alignment. Damage on mobilebearing surfaces was positively correlated with length of implantation and was greater in implants removed for osteolysis or instability than in those removed for stiffness or infection. Conclusions Each bearing surface in mobile-bearing implants was damaged to an extent similar to that in fixedbearing implants, making the combined damage score higher than that for fixed-bearing implants. Mobile-bearing TKAs did not improve wear damage, providing another argument against the superiority of these implants over fixed-bearing implants.

Section: Discussionsupporting

confidence: 91%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Wear Damage in Mobile-bearing TKA is as Severe as That in Fixed-bearing TKA

Kelly

Wright

et al. 2011

“…Therefore, clinical performance of knee bearings is often based on visual assessment of bearing surfaces rather than actual material lost [7,8,10]. Rather than surface deformation features, it is the polyethylene debris from both the abrasive and adhesive wear on the backside surface of the tibial inserts that is implicated as a cause for wear debris osteolysis [11,13].…”

Section: Discussionmentioning

confidence: 99%

Does Increased Topside Conformity in Modular Total Knee Arthroplasty Lead to Increased Backside Wear?

Schwarzkopf

Scott

Carlson

et al. 2015

Background Modular metal-backed tibia components allow surgeons intraoperative flexibility. Although it is known that modular tibia components introduce the possibility for backside wear resulting from relative motion between the polyethylene insert and the tibial baseplate, it is not known to what degree variability in the conformity of the tibial polyethylene liner itself might contribute to backside wear. Questions/purposes The purpose of this study was to determine whether a flat, cruciate-retaining tibial polyethylene bearing generates less backside wear than a more conforming (curved) tibial polyethylene bearing in an analysis of specimens explanted during revision surgery. MethodsThe study included 70 total knee inserts explanted at revision surgery, all implanted and explanted by the same surgeon. Two different cruciate-retaining insert options in an otherwise similar knee system were used: one with a curvedon-flat (17) articular geometry and one with a highly conforming curved-on-curved design (53); both groups were sequential cohorts. The composite backside wear depth for the insert as well as the volume of backside wear was measured and compared between groups. Results The median linear backside-normalized wear for the posterior lipped inserts was 0.0063 mm/year (range, 0-0.085 mm/year), which was lower than for the curved inserts at 0.05 mm/year (range, 0.00003-0.14 mm/year) (p \ 0.001). The median calculated volumetric backsideOne of the authors (RS) has received consulting fees from Smith & Nephew (Memphis, TN, USA) (less than USD 10,000). One of the authors (RDS) has received consulting fees from DePuy (Warsaw, IN, USA) (less than USD 10,000) and royalties from DePuy (greater than USD 1,000,000). One or more of the authors (EMC, JHS) has received institutional funding from DePuy, ConforMIS (Bedford, MA, USA), and Biomet (Warsaw, IN, USA). All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research 1 editors and board members are on file with the publication and can be viewed on request. Clinical Orthopaedics and Related Research 1 neither advocates nor endorses the use of any treatment, drug, or device. Readers are encouraged to always seek additional information, including FDAapproval status, of any drug or device prior to clinical use. Each author certifies that his or her institution approved the human protocol for this investigation, that all investigations were conducted in conformity with ethical principles of research, and that informed consent for participation in the study was obtained. This work was conducted at the New England Baptist Hospital, Boston, MA USA. The biomechanical material analysis was conducted at the Thayer School of Engineering, Dartmouth College, Hanover, NH, USA. Conclusions In this retrieval study, more conforming tibial inserts demonstrated more backside-normalized wear than the flatter designs. This suggests that in this modular total knee arthroplasty design, higher articular conformity to address the issues of high bear...

“…However, measures of condylar penetration do not allow an analysis of penetration volume and are not necessarily an accurate measure of true wear because penetration does not account for creep or deformation. Analysis of retrieved components either at revision or postmortem allows the analysis of surface damage and changes in polyethylene thickness [4,7,8,[10][11][12]16]. Retrieval analysis is inherently more accurate and detailed than radiographic analysis of condylar penetration and does provide more insight into wear.…”

Section: Introductionmentioning

confidence: 99%

Can Microcomputed Tomography Measure Retrieved Polyethylene Wear? Comparing Fixed-bearing and Rotating-platform Knees

Engh

Zimmerman

Hopper

et al. 2013

Background Wear of total knee polyethylene has been quantified gravimetrically with thickness measurements and evaluation of surface wear modes. However, these techniques do not localize volumetric wear. Questions/Purposes We used micro-CT scans of retrieved total knee liners and unworn, new liners to determine the volume and location of wear. Methods We retrieved 12 fixed and 12 rotating-platform bearings after a mean 52 months of use. Inserts were weighed and thickness was measured. Micro-CT scans of retrieved and matched new liners were superimposed to compare the location and magnitude of wear. Results The average total wear was 254 ± 248 mm 3 . The average wear rate was 58 ± 41 mm 3 /year. Wear was 69% of penetration, demonstrating the contribution of deformation to knee wear. Rotating-platform wear rate was 43 ± 25 mm 3 /year and the fixed-bearing rate was 74 ± 49 mm 3 /year. Five percent of the rotating-platform wear rate came from the backside compared with 14% of the fixed-bearing wear rate. Conclusions Micro-CT can determine the volume and location of wear of retrieved tibial liners. Because the magnitude of the manufacturing tolerances was approximately half the magnitude of the total wear on average, accounting for the potential influence of tolerances is important to accurately measure volumetric wear if the unworn (preimplantation) geometry of the insert is unknown. Without accounting for tolerances, this technique may not be applicable for retrievals with a short followup that have low wear. However, application of micro-CT could be of value in determining the exact location of wear in knee simulator studies in which the same insert is measured repeatedly and manufacturing tolerances are not a concern.